StuckAgainSteve
Well-Known Member
It would be easy enough to prove either way - get a 'scope or a decent logging voltmeter on the output of the driver pack. I'd be bloody surprised if they were as fancy as pulsing voltages to soften the valve closure - but then Land Rover do have a habit of spending money in the wrong areas!
StuckAgainSteve
Well-Known Member
The last tail doesn't look any different to me to the other decays other that it was allowed to complete - perhaps there's a big cap in there and that's what we're seeing? It looks like the voltage is held to energise the solenoid and then pulsed to hold it. I'd expect to see the amplitude of the pulses to change for an attempt at a soft close (if that's possible) there doesn't seem to be any modulation of the pulses other than the initial start up. Perhaps the big cap is an attempt at a soft close? I'm not convinced it would have that effect but it's possible I suppose! Presumably the cap would be needed anyway to stop the solenoid closing between pulses.
The final tail shows a slow decay to lower the valve onto the seat.
StuckAgainSteve
Well-Known Member
If you cut the final decay trail at the same width after the other pulses you'll see there's no difference other than the delay is allowed to continue (voltage has been cut off) whether this is to "soft close" the solenoid or not is open to debate - I suspect there's a capacitor there to smooth out the pulsing required to limit current to the solenoid after initial activation. If I was coding an attempt to soft close I would have tailed off the pulses in order to drop the amps in a uniform manner. The pulses just stopped - IMHO the tail is merely incidental. No proof either way but very interesting none-the-less.
If you cut the final decay trail at the same width after the other pulses you'll see there's no difference other than the delay is allowed to continue (voltage has been cut off) whether this is to "soft close" the solenoid or not is open to debate - I suspect there's a capacitor there to smooth out the pulsing required to limit current to the solenoid after initial activation. If I was coding an attempt to soft close I would have tailed off the pulses in order to drop the amps in a uniform manner. The pulses just stopped - IMHO the tail is merely incidental. No proof either way but very interesting none-the-less.
There is literature that states a soft close takes place just can't find it. Logic says it must be so, after all if the solenoid shaft was left to return under spring pressure how long would the rubber seal last. I disagree, the other traces show a cut off point where voltage ceases and returns immediately to zero. The third trace shows a gradual decline in amperage in the coil after power off allowing for a soft close.
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tomcat59alan
Well-Known Member
Datatek
Well-Known Member
There is no capacitor. You cannot soft close a spring return solenoid without some pretty fancy modulation.If you cut the final decay trail at the same width after the other pulses you'll see there's no difference other than the delay is allowed to continue (voltage has been cut off) whether this is to "soft close" the solenoid or not is open to debate - I suspect there's a capacitor there to smooth out the pulsing required to limit current to the solenoid after initial activation. If I was coding an attempt to soft close I would have tailed off the pulses in order to drop the amps in a uniform manner. The pulses just stopped - IMHO the tail is merely incidental. No proof either way but very interesting none-the-less.
Datatek
Well-Known Member
Coming from a man who could not get his head round the workings of the D+ line on the alternator/fuel pump relay that's a bit of a sweeping statement. I will have proof of that shortly as I have repaired the drive pack in question. If it works reliably then it will be reasonable proof of noise effects causing the problem.
As I said, you are very selective in what you choose to read and believe.
I like to prove things for myself.
Datatek
Well-Known Member
It's a current wave form not voltage and quite clearly shows the intial pick pulse and the hold pulse train follwed by shut off.
The six solenoid valves are relatively large because of the response time required by the
system. If these solenoid valves were operated for long periods of time under conditions of
high temperature or high currents, they would overheat and fail. To prevent this, the valve
driver controls the amount of current that flows through each solenoid coil. Because the
current required to open the solenoid is considerably higher than the current required to hold
the solenoid open, a hit and drop signal is used. Upon a valve open request the control
voltage is near 0V for 0.050 seconds (50 milliseconds) then is pulsed to limit current through
the coil. The pulsed voltage will read approximately 9 volts with a high impedance DVOM or
can be viewed with an oscilloscope to be a 24 KHz 12-volt square waveform. The steady
state current passing through each coil is approximately 1 amp.system. If these solenoid valves were operated for long periods of time under conditions of
high temperature or high currents, they would overheat and fail. To prevent this, the valve
driver controls the amount of current that flows through each solenoid coil. Because the
current required to open the solenoid is considerably higher than the current required to hold
the solenoid open, a hit and drop signal is used. Upon a valve open request the control
voltage is near 0V for 0.050 seconds (50 milliseconds) then is pulsed to limit current through
the coil. The pulsed voltage will read approximately 9 volts with a high impedance DVOM or
can be viewed with an oscilloscope to be a 24 KHz 12-volt square waveform. The steady
Not according to Land rover it isn't. It is an alternative fault code which can be misinterpreted by the ECU if the driver pack fails to carry out a command for various reasons. One cause could be a faulty driver pack for sure, by not always.
Datatek
Well-Known Member
Exactly so. If there is a component failure causing electrical interferance and the command fails.
Ok the amperage decay then, either way the seal is being lowered onto the seat rather than head butting the bloody thing.
StuckAgainSteve
Well-Known Member
Okay there's no cap, can the solenoid coils themselves retain current momentarily or does the movement of the magnet in the windings generate current? And yes your point about modulation is the one I was making earlier - I see no evidence of modulation of the current to effect a soft close, the "hold" pulse just stops.
Datatek
Well-Known Member
Look at it again, after the pick pulse of 3 amps, the current is a stream of pulses at a constant average level of 1 amp to hold until it turns off. As I said, pulse and hold.
There is no modulation and a spring return solenoid armature is effectively a snap action device, it stays held until the magnetic field reduces to a point where it cannot overcome the spring then it snaps shut. Air pressure may affect the speed of closing, I know not, but electronics do not as proved by the information you posted.
LR also mention the requirement for rapid response, a slow close would go against that.
Datatek
Well-Known Member
No apart from the normal back EMF of inductor decay which is damped to protect the MOSFET.
And could that allow the valve to drop more gently. Because something does.
